Tension control system for a running web

ABSTRACT

Constant longitudinal tension is maintained on a running web of cloth or the like by means of a variable speed motor and control system. A pivotally mounted feeler rod rides against the web and is angularly moved by changes in web tension. The angular motion is employed to operate a variable potentiometer forming part of a motor speed control circuit. The motor drives a draft roll and the motor speed is responsive to the potentiometer through an SCR feedback control circuit.

United States Patent 1191 Holm Apr. 30, 1974 [54] TENSION CONTROL SYSTEM FOR A 2,544,467 3/l95l Michel 226/44 X RUNNING WEB 3,087,663 4/1963 Anderson 226/44 [75] Inventor: WIIham J. Holm, Sprmgfield, Vt Primary Examiner Richard A. Schacher [73] Assignee: Riggs & Lombard, lnc., Lewell, Attorney, Agent, or Firm-Morse, Altman, Oates &

Mass. Belk,

[22] Filed: Oct. 24, 1972 21 Appl. No.: 299,709 [57] ABSTRACT Constant longitudinaltension is maintained on a running web of cloth or the like by means of a variable (gill. 226g62gh2iggg Speed motor and comm] systmn A pivotally mounted [58] Fieid /44 25 42 feeler rod rides against the web and is angularly moved by changes in web tension. The angular motion 56] References Cited is employed to operate a variable potentiometer forming part of a motor speed control circuit. The motor 1 UNITED STATES PATENTS drives a draft roll and the motor speed is responsive to 1,696,386 12/1928 Corey 226/42 the potentiometer through an SCR feedback control 1,758,794 5/1930 Hoxie.... 226/44 x circuit 1 1,791,450 2/1931 Kellogg. 226/42 x Y 1 2,278,136 3/1942 Otis 226/42 x Y 4 Claims, 2 Drawing Figures POWER SUPPLY SUMMING CIRCUIT PATENTEI] APR 3 0 I974 RECTIFIER AMPLIFIER I3 4 SUMMING CIRCUIT POWER SUPPLY ISUMMING CIRCUIT Fig.2

TENSION CONTROL SYSTEM FOR A RUNNING WEB BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to means for maintaining a constant tension on a running web and more particularly is directed towards a new and improved tension-sensing and motor speed control circuit for use in textile machinery.

2. Description of the Prior Art In processing various types of webs, particularly in the textile field, it is generally desirable to maintain a constant longitudinal tension on the web as it moves along. Changes in tension, particularly during certain processes, can adversely affect the quality of the finished product. In the past, a variety of different techniques have been employed in an attempt to maintain uniform and constant longitudinal tension in a running web. Such techniques have included mechanical clutching arrangements synchronized motors and the like. However, these systems have not been entirely satisfactory from the standpoint of speed control, sensitivity to local variations in tension and reliability.

Accordingly, it is an object of the present invention to provide improvements in tension control systems for a running web. Another object of this invention is to provide a web tension maintenance system adapted to be operated over a wide range of speeds and one that is fully responsive to sudden changes in tension.

SUMMARY OF THE INVENTION This invention features a system for maintaining constant tension on a running web, comprising a plurality of draft rolls engaging the web, a variable speed DC motor drivingly connected to each draft roll, an SCR motor speed control system, a variable potentiometer connected to each motor field and a tension-sensing member engaging said web and drivingly connected to the potentiometer to vary the voltage in the field circuit in response to changes in tension and thereby provide compensating changes in speed in response to localized changes in tension.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in perspective, somewhat schematic, of a web tension control system made according to the invention, and,

FIG. 2 is a diagram of the rectifier circuit employed in the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, the reference character indicates a web such as a woven or knit material carried in a flat condition in the direction of the arrow by means of a draft roll 12 driven by a variable speed DC motor 14. The speed of the motor 14 is controlled automatically by means of a web tension-sensing apparatus generally indicated by the reference character 16 and comprised of a pivotally mounted support 20 extending transversely above the web 10 and a parallel web-engaging feeler rod 22 suspended therefrom by means of rigid connecting arms 24. The feeler rod 22 rides against a break in the web 10 so as to pivot the rod 22 about its support axis depending upon an increase or decrease in the longitudinal tension in the web 10. The support 20 and the feeler rod 22 are biased into contact with theweb 10 by means of a counterbalancing weight 26 fixed to and projecting radially from a shaft 28 extending from the end of the rod 20. The shaft 28 also carries a gear 30 drivingly connected by a chain belt 32 to a pinion gear 34. The pinion gear 34, in turn, is drivingly connected by a stub shaft 36 to the wiper arm of a rotary, variable potentiometer 38. In this fashion, any change in the tension of the web will move the feeler arm and thereby move the wiper arm of the potentiometer. The potentiometer 38 is part of a circuit connected to a power supply 40 the output of which is controlled by a manually operated variable potentiometer 42 and a vernier potentiometer 44. The potentiometers 42 and 44 are employed to control the voltage to the armature of the motor 14. The potentiometer 42 is mechanically ganged to one or more similar potentiometers 42, each electrically connected to a vernier potentiometer 44' for the armature control of other motors 14' whereby a' number .of independently driven motors, each connected to its own draft roll 12,12, may be operated at the same speed, the armature voltages being manually adjusted in unison to provide a synchronous system. The vernier potentiometers 44 are independent to allow for minor adjustments in the speeds of the several motors.

The function of the potentiometer 38 is to provide independent speed control over the motor I4 apart from all other motors that may be utilized in a synchronized drive system by automatically changing the field voltages of the motors. In this fashion, local changes or differences in tension in the web may be corrected automatically by increasing or decreasing the speed of one motor without altering the speed of 'the other motors. The output of the potentiometers 42 and 44 is through a lead 46 to a summing circuit 48. The summing circuit receives a feedback signal-from the motor 14 through a lead 50, which signal-is the motor armature voltage feedback and is compared in the summing circuit48 with a reference voltage from the potentiometers 42 and 44. The output of the summing circuit 48 thus is an error voltage which is fed into an amplifier 52 having an output to a rectifier circuit 54 adapted to generate firing pulses to the motor 14.

The rectifier circuit 54' employed in FIG. 1 is shown in greater detail in FIG. 2 and employs a pair of silicon controlled rectifiers (SCR)'56 and 58, each connected in parallel across the armature of the motor 14 and each serially connected to a silicon diode and 62, respectively, by leads 64 and 66, respectively. The circuit is energized by means of leads 68 and 70, each having a fuse 72 and 74.

The circuit operates on a basis that the speed of a DC motor may be controlled by varying the armature voltage while keeping the field voltage constant. The armature is supplied with variablevoltage power by the silicon controlled rectifiers 56 and 58 connected in a full wave circuit shown in FIG. 2, forms a full wave bridge circuit. During one half cycle of line voltage alternation, the current flows from one side of the line through the fuse72, the SCR 58, the armature of the motor 14, the diode 60 and the fuse 74. During the next half cycle the current flows through the fuse 74, the SCR 56, the armature of the motor, the diode 62 and the fuse 72. Note that the flow of current through the armature is in the same direction during both half cycles. To control the speed of the motor, the output of this rectifier combination must be varied. This is done by the SCRs 56 and 58 which have the ability to hold off conduction of current and therefore control the voltage to the motor.

The rectifier circuit discussed above also includes a source of constant excitation for the motor field 45-. The circuit utilizes the diodes 60 and 62 and by connecting the motor field 45, as shown in H0. 2, these two diodes act as a half-wave, back-rectifier circuit. During one-half cycle of line alteration, current flows from one side of the line through the fuse 72, the motor field 45, the diode 60 and the fuse 74 to the other side of the line. During the next half cycle, the diode 60 blocks the flow of current from the line. The motor field 45 is an inductive load and discharges its stored energy through the diode 62 during this half cycle. The current through the field 45 is seen to be unidirectional. The voltage level in the field is, of course,

controlled by the potentiometer 38 which responds to:

web tension.

The SCRs 56 and 58 require pulse signals to turn on at the proper time for a given armature voltage level. These pulses are formed in the control circuit described below. The control circuit includes the power supply 40 and the amplifier circuit 52 as shown in FIG. l.-'The power supply changes an AC input voltage to a DC voltage. The potentiometer 42 across this voltage is used to set the reference voltage. Armature voltage is used as a feedback voltage to be compared to the reference voltage. Thesetwo voltages are added together in the summing circuit 48 in such a way that any difference between the two appears 'at the amplifier 52. if the motor is running at thespeed called for by the reference voltage, the feedback voltage is nearly equal to the reference voltage. If the motor is not running at the speed called for by the reference voltage there will be a difference between the feedback and reference voltages. This difference is called the error voltage signal and the magnitude of this error reflects the difference between actual motor speed and desired motor speed. The amplifier then converts the error signal to firing pulses that turn on the SCRs at the proper instants to correct any error in motor speed.

With the above system, a number of motors may run at the same speed and yet means are provided for compensating for any variable in the system or in the fabric to prevent any stretching or looseness in the system. Using the tension-sensing and speed control system shown, the individual motors may be sped up or slowed down independently of the other motors and thereby insure uniform tension throughout the entire system.

Having thus described the invention, what I claim anddesire to obtain by Letters Patent of the United States is:

l. A tension control system for a running web, comprising a. a plurality of spaced draft rolls drivingly connected to said web,

b. a variable speed DC motor drivingly connected to each of said draft rolls,

c. a first variable potentiometer operatively connected to, the armature circuit of each of said motors and to a power source,

d. all of said first potentiometers being interconnected for simultaneous adjustment thereof,

e. a second variable potentiometer operatively connected to the field circuit of each of said motors and to a power source,

f. tension sensing means responsive to changes in web tension and operatively connected to each of said second potentiometers for changing the speed of an individual motor and draft roll independently of the other motors and draft rolls, and,

g. voltage control means connected to each of said motors and including a pair of silicon controlled rectifiers in a full wave bridge circuit connected between said armature and said first potentiometer and feedback means from said armature for controlling the output of. said circuit and a summing circuit connected to said feedback means and to said first potentiometer for generating an error signal representing the'difference between the armature voltage and the voltage from said first potentiometer.

2. A tension control system according to claim 1 wherein each of said tension sensing means includes a feeler rod 'mounted for angular movement across a break in the direction of said web whereby said rod will move in response to a change in web tension and coupling means connecting said rod to said second potentiometer.

3. A tension control system according to claim 2 wherein said coupling means includes a first rotary shaft supporting said rod, a first gear mounted to said first shaft, a second rotary shaft drivingly connected to said second potentiometer, a second gear mounted to said second shaft; and an endless chain in mesh with both gears.

4. A tension control system according to claim 1 including an independently operated vernier potentiometer in circuit with each of said first potentiometers. 

1. A tension control system for a running web, comprising a. a plurality of spaced draft rolls drivingly connected to said web, b. a variable speed DC motor drivingly connected to each of said draft rolls, c. a first variable potentiometer operatively connected to the armature circuit of each of said motors and to a power source, d. all of said first potentiometers being interconnected for simultaneous adjustment thereof, e. a second variable potentiometer operatively connected to the field circuit of each of said motors and to a power source, f. tension sensing means responsive to changes in web tension and operatively connected to each of said second potentiometers for changing the speed of an individual motor and draft roll independently of the other motors and draft rolls, and, g. voltage control means connected to each of said motors and including a pair of silicon controlled rectifiers in a full wave bridge circuit connected between said armature and said first potentiometer and feedback means from said armature for controlling the output of said circuit and a summing circuit connected to said feedback means and to said first potentiometer for generating an error signal representing the difference between the armature voltage and the voltage from said first potentiometer.
 2. A tension control system according to claim 1 wherein each of said tension sensing means includes a feeler rod mounted for angular movement across a break in the direction of said web whereby said rod will moVe in response to a change in web tension and coupling means connecting said rod to said second potentiometer.
 3. A tension control system according to claim 2 wherein said coupling means includes a first rotary shaft supporting said rod, a first gear mounted to said first shaft, a second rotary shaft drivingly connected to said second potentiometer, a second gear mounted to said second shaft, and an endless chain in mesh with both gears.
 4. A tension control system according to claim 1 including an independently operated vernier potentiometer in circuit with each of said first potentiometers. 